The invention relates to a wheel drive, in particular for mobile machines, having an integrated dynamic service brake.
Mobile machines, such as fork-lift trucks, forest machines, agricultural machines, etc., are usually moved at speeds of up to 40 km/h. A high degree of manoeuvrability is required with such machines. For these reasons, it has become customary for mobile machines to have direct wheel drives, as opposed to a central drive in which the driving force is transmitted to a pair of wheels. Because the mobile machines of the type in question here already have a hydraulic circuit for moving their working equipment, an adjustable hydraulic motor, which can advantageously be operated with the existing hydraulic circuit, is preferably used as the drive element in the wheel drive.
A wheel drive of the generic type is known from DE 299 10 017 U1. The wheel drive has a carrying axle which is funnel-shaped in the region near to the vehicle and is attached fixed in terms of rotation to the frame of a vehicle. On the carrying axle there is a wheel hub which is mounted so as to be capable of rotating by means of roller bearings. The vehicle wheel can be attached to the wheel hub. The wheel hub is driven by a drive shaft running in the centre of the carrying axle, via a planetary gear mechanism which reduces the rotational speed. The planetary gear mechanism is therefore connected at the input end via its central sun wheel to the drive shaft. At the output end, the planetary wheels are connected directly to the wheel hub, which forms the planetary carrier here.
A dynamic service brake for the wheel drive acts via the outer ring gear of the planetary gear mechanism. The dynamic service brake is embodied as a multidisc brake whose stationary discs are connected to the wheel hub and whose moving discs are connected to the ring gear of the planetary gear mechanism via a ring-carrier. Braking while the wheel drive is operating is carried out by applying pressure medium to a piston which presses the stationary and moving brake discs axially one against the other in order to bring about effective braking of the vehicle, there being an arrangement of alternating stationary and moving discs.
The heat produced during the braking operation is conveyed into the oil bath and conducted away to the outside via the wheel hub. Because of the arrangement of the dynamic service brake at the outer radius in the centre of the wheel hub, the maximum generation of heat occurs in the region where the vehicle wheel is attached. In this region, the conduction of heat away to the outside is unfavourable, that when the service brake experiences extreme stressing the entire wheel drive may overheat. Furthermore, it is disadvantageous that when the wheel drive is serviced or repaired it is necessary to completely dismount the planetary casing. This is possible only when the vehicle wheel has previously been dismantled.
A further wheel drive is known from EP 0 684 401 B1. In contrast to the wheel drive described above, a disc brake is used here as the dynamic service brake. However, the brake disc of the disc brake with its brake shoes which can be activated hydraulically are also arranged in the centre of the wheel drive so that the heat generated by the service brake cannot easily be conducted away to the outside. The planetary gear mechanism for transmitting the driving force from the drive shaft to the wheel hub is also placed at the distal end of the wheel drive here. For servicing and repair purposes, the dynamic service brake and the planetary gear mechanism are also only accessible when the wheel is removed and the pot-shaped housing cap dismounted.
The object of the present invention is to improve further the wheel drive of the generic type to the effect that service-friendly and repair-friendly access to the essential components of the brake and gear mechanism is possible and the risk of overheating of the wheel drive during operation is minimized.
The invention includes the technical teaching that the dynamic service brake of a wheel drive is arranged within the ring gear forming the wheel hub, at the end directly behind a detachable gear mechanism cover and at the outer radius on a hollow-cylinder-shaped brake carrier forming the end piece with carrying axles which are fixed in terms of rotation, the planetary gear mechanism of the service brake being arranged within the ring gear following in the direction of the vehicle frame.
The arrangement according to the invention of the brake components and the mechanism components of the wheel drive is made possible by means of the specific configuration of the brake carrier which represents a prolongation of the carrying axle which is fixed in terms of rotation. As a result, the service brake extends to the distal end of the wheel drive. At this point, as a result of the slipstream, there is improved conduction away of heat directly in the region of the wheel drive in which the braking heat is generated, resulting in improvement to the cooling of the wheel drive. Because the wheel drive is sealed off by means of a flat, end-mounted gear mechanism cover, simple accessibility of the essential components when performing servicing or repairs is ensured. There is no need to remove the vehicle wheel for this purpose.
In order to ensure a space-saving gear mechanism function of the planetary gear mechanism within the wheel drive, the drive-end sun wheel preferably engages with planetary wheels which are secured fixed in terms of rotation to the carrying axle by means of planetary bolts. The planetary wheels roll in turn on an inner toothing which is provided directly on the inner radius of the ring gear.
It is also possible to provide a further preliminary stage of the gear mechanism within the wheel drive in order to convert a desired transmission ratio appropriately for the loading. Preferably, at least one preliminary stage of the gear mechanism is positioned within the hollow-cylinder-like brake carrier, directly behind the detachable gear mechanism cover and thus also in an easily accessible location. The preliminary stage of the gear mechanism is connected at the input end to the drive shaft of the wheel drive and at the output end to the sun wheel of the (main) planetary gear mechanism which is connected downstream in this respect. The preliminary stage of the gear mechanism may be embodied as a single-stage or multistage preliminary planetary gear mechanism. Because of its coaxial design, the arrangement as a planetary gear mechanism is particularly suitable for this. For example, the ring gear of a single-stage preliminary planetary gear mechanism can easily be embodied by means of the gear mechanism cover so as to be fixed in terms of rotation with respect to the ring gear, forming the wheel rim, of the (main) planetary gear mechanism. Due to this, the ring gear of the preliminary stage of the gear mechanism is fitted with at least one or two planetary wheel sets. These planetary wheel sets are preferably arranged behind a separate cover which is arranged coaxially in the gear mechanism cover and which also forms a securing means for the entire drive shaft of the wheel drive.
In addition to the service brake which is activated while travelling, a second brake may also be provided at the input end on the drive shaft, said second brake performing the function of a hand brake, that is to say the function of keeping the vehicle stationary when it is parked.
The invention accordingly comprises the features of construction, combination(s) of elements, and arrangement of parts which will be exemplified in the construction(s) hereinafter set forth, and the scope of the invention will be indicated in the claims.